Heavy ion transient characterization of a hardened-by-design active pixel sensor array

This paper presents heavy ion test data on the single event transient response of an active pixel sensor four quadrant test chip with different radiation tolerant designs in a commercial 0.35 μm CMOS process. The physical design techniques of enclosed geometry and P-type guard rings are used to design the four N-type active photodiode pixels as described in a previous paper (EI-Sayed Eid et al, IEEE Trans. Nucl. Sci., Vol. 48, pp. 1796-1806, Dec. 2001). Transient measurements on the 256×256 pixel array as a function of Ar ion incidence angle show a significant variation in the amount of charge collected as well as the charge spreading dependent on the pixel type. The results are correlated with processing and design information provided by Photobit. In addition, there is a significant variability between individual ion strikes for some unit cell designs. No latch-up is observed up to an LET (linear energy transfer) of 106 MeV/mg/cm².